Usain Bolt, the world’s fastest person, ran a 100-meter sprint at a speed of 37.57 kilometers per hour. That’s mind-blowingly fast for a human. It’s about the same speed as cruising in a car through your neighborhood or in a school zone. It might not seem that fast when you’re in the car, but for a person? Few runners in the world can even come close.

There are several reasons why some people can run very fast while others tend to run more slowly. Genetics — the traits you inherit from your parents — play a role, but so do your choices and experiences.

One major factor that influences your ability to run fast is the structure of your body, including how your muscles work.

The human body has more than 600 muscles that work together, allowing you to move in different directions and at various speeds. These muscles are made up of groups of fibers. There are two main types: fast twitch and slow twitch.

Muscles have different mixes of these fiber types. For example, two muscles make up the calf: One is predominantly fast twitch — that’s the gastrocnemius, used for sprinting and jumping. The other is mostly slow twitch — that’s the soleus, used for walking and jogging.

Fast-twitch muscle fibers are larger and help your body move quickly and generate significant force. Sprinters tend to have an abundance of fast-twitch muscle fibers. However, this muscle fiber type also tires quickly, which limits how long you can run at top speed to relatively short distances.

Slow-twitch muscle fibers are smaller and help you run at slower speeds, but with greater endurance. Long-distance runners and competitive cyclists tend to have a lot of these muscles.

How much you have of each type of muscle fiber — fast twitch and slow twitch — is mostly determined by your genes, so you’ll have to work with what you’re born with when it comes to muscle types. But exercises can help train those muscles.

Physical ability isn’t just about muscle. Your brain plays an important role, too. Your skeletal muscles are controlled by your brain — you think about your actions and then execute the movements. For example, you can control how long your stride is, how your arms move, how your feet hit the ground and even the techniques you use to breathe.

You can teach your body to use the best running techniques. That includes proper posture, so your body is standing tall, and an economical stride, so your feet land below you rather than too far out in front, where they can slow you down.

You can also improve your running form by using your whole body, with your arms pumping in opposition to the legs, running on your toes and maximizing the time spent in flight phase with both feet off the ground. Using proper running techniques helps the muscles create more force and work together, which helps you run faster.

Words to Learn 相关词汇

【巡航】xúnháng cruise travel smoothly at a moderate speed

【一大步】yīdàbù stride a long step

世界上跑得最快的人是尤塞恩•博尔特，他百米短跑的速度为每小时37.57公里。

对于人类而言，这个速度快得惊人。这大约相当于在社区或学校周边区域开车的速度。坐在车里的人可能不觉得车跑得有多快，但对于人来说就大不一样。世界上很少跑者能接近这个速度。

几个原因可以解释为什么有些人跑得非常快，而其他人则跑得比较慢。来自父母的遗传基因是一个因素，但怎样跑和经验也会有影响。

影响快速奔跑能力的一个主要因素是身体结构，包括肌肉是如何工作的。

人体有600多块肌肉协同工作，让你能向不同方向、以不同速度运动。这些肌肉由不同肌纤维群组成，主要有两种类型：快肌纤维和慢肌纤维。

肌肉由不同类型的纤维群共同组成。例如，小腿由两块肌肉组成：一块主要是快肌纤维 —— 腓肠肌，用于短跑和跳跃；另一块主要是慢肌纤维 —— 比目鱼肌，用于走路和慢跑。

快肌纤维较大，帮助身体快速移动并产生巨大的力量。短跑运动员往往有大量快肌纤维。然而，这种肌肉纤维类型很容易疲劳，限制了能以最高速度跑步的时长，只能跑完相对较短的距离。

慢肌纤维较小，帮助人以较慢的速度、更强的耐力跑步。长跑运动员和竞技自行车手往往有大量这类肌肉。

人拥有不同种肌肉纤维 —— 快肌纤维和慢肌纤维 —— 的数量主要由基因决定，所以你将不得不使用你出生既定拥有的肌纤维。但是锻炼可以帮助训练这些肌肉。

身体能力不仅仅关乎于肌肉。大脑也扮演着重要角色。

骨骼肌由大脑控制 —— 你在行动前思考，然后执行动作。例如：步幅有多大、手臂如何摆动、脚如何接触地面，甚至呼吸技巧，这些都可以控制。

可以学习使用最佳跑步技术。这包括正确的姿势：身体挺直，步幅合理，让脚落在身体下方而不是太靠前 —— 这样会减慢速度。

还可以通过全身协调来改善跑步姿势，让手臂与腿部交替摆动，用脚尖跑步，并最大限度地延长双脚离地的“飞行”时间。使用正确的跑步技术有助于肌肉产生更多力量并协同发力，有助于跑得更快。(chinadaily.com.cn)